Not Applicable
Not Applicable
1. Field of the Invention
This invention is in the field of methods and apparatus used to generate and control the delivery of cryosurgical refrigeration power to a probe or catheter.
2. Background Information
In a cryosurgical system, contaminants such as oil, moisture, and other impurities are often deposited in the impedance tubing or other restriction through which the refrigerant is pumped. In the impedance tubing, the temperature is very low, and the flow diameter is very small. Deposit of these impurities can significantly restrict the flow of the cooling medium, thereby significantly reducing the cooling power.
A cryosurgical catheter used in a cardiac tissue ablation process should be able to achieve and maintain a low, stable, temperature. Stability is even more preferable in a catheter used in a cardiac signal mapping process. When the working pressure in a cryosurgery system is fixed, the flow rate can vary significantly when contaminants are present, thereby varying the temperature to which the probe and its surrounding tissue can be cooled. For a given cryosurgery system, there is an optimum flow rate at which the lowest temperature can be achieved, with the highest possible cooling power. Therefore, maintaining the refrigerant flow rate at substantially this optimum level is beneficial.
In either the ablation process or the mapping process, it may be beneficial to monitor the flow rates, pressures, and temperatures, to achieve and maintain the optimum flow rate. Further, these parameters can be used to more safely control the operation of the system.
A cryosurgical system which is controlled based only upon monitoring of the refrigerant pressure and catheter temperature may be less effective at maintaining the optimum flow rate, especially when contaminants are present in the refrigerant. Further, a system in which only the refrigerant pressure is monitored may not have effective safety control, such as emergency shut down control.
It may also be more difficult to obtain the necessary performance in a cryosurgery catheter in which only a single compressor is used as a refrigeration source. This is because it can be difficult to control both the low and high side pressures at the most effective levels, with any known compressor. Therefore, it can be beneficial to have separate low side and high side pressure control in a cryosurgical system.
Finally, it is beneficial to have a system for monitoring various parameters of data in a cryosurgery system over a period of time. Such parameters would include catheter temperature, high side refrigerant pressure, low side refrigerant pressure, and refrigerant flow rate. Continuous historical and instantaneous display of these parameters, and display of their average values over a selected period of time, can be very helpful to the system operator.
The present invention provides methods and apparatus for controlling the operation of a cryosurical catheter refrigeration system by monitoring pressures, temperature, and/or flow rate, in order to automatically maintain a stable refrigerant flow rate at or near an optimum level for the performance of crysurgical tissue ablation or mapping. Different refrigerant flow rates can be selected as desired for ablation or mapping. Flow rate, pressures, and temperature can be used for automatic shut down control. Refrigerant sources which provide separate high side and low side pressure controls add to the performance of the system. Continuous displays of temperature, high side refrigerant pressure, low side refrigerant pressure, and refrigerant flow rate are provided to the operator on a single display, to enhance system efficiency and safety.
The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which: